Thin layer catalysts based on Raney alloys, and method for the production thereof

ABSTRACT

Raney alloy catalysts applied to a support are described, said catalysts having an extremely thin layer of Raney alloy with a thickness of 0.01 to 100 μm. These catalysts are prepared by vapor deposition of the appropriate metals under reduced pressure. They are generally suitable for all known hydrogenation and dehydrogenation reactions and are extremely abrasion-resistant.

The present invention relates to the field of heterogeneous catalysis.More precisely, the present invention relates to heterogeneous catalystsbased on Raney alloys applied to knitted or woven fabric tapes.

Raney alloys as they are known, especially Raney nickel, have been knownfor a long time as heterogeneous catalyst systems. They are used forhydrogenations or dehydrogenations. These alloys are intermetallicphases, for example, in the case of Raney nickel, phases with thecomposition Ni₂Al₃ or NiAl₃. Conventionally these alloys are used in theform of fine powders suspended in the solution in which the reaction iscarried out. The aluminum is dissolved out by treatment with lyes togive a very active Ni catalyst.

Raney nickel, in particular, is a very active catalyst forhydrogenations or dehydrogenations, although there are a number ofdisadvantages arising from the powder form of the catalyst. Thus, one isoften confronted with problems of catalyst distribution in the reactor;also, the residence times of the reactants in the reactor are frequentlycritical. In addition, when the reaction is complete, the powder has tobe separated off, generally by filtration, which demands an elaborateand expensive work-up technology.

For this reason, attempts have been made to prepare fixed bed catalystswhich contain typical Raney nickel alloys, but not in powder form. Inthe simplest case, shaped articles are produced from the fine suspensionpowders.

This is described for example in U.S. Pat. No. 4,826,799, where an alloypowder is mixed with polyethylene and a binder and compressed to shapedarticles in screw extruders. In the subsequent calcination step, therequired intermetallic phases are formed and the polyethylene is burntoff at the same time to give solid strands which are suitable as ahydrogenation catalyst, especially for the hydrogenation of toluene.

Another possibility is to prepare catalysts in which a Raney alloysurface is applied to a woven fabric.

This is described for example in EP-A-91 028, which discloses catalystswith fabric components having an integrated Raney nickel surface. Thesecatalysts are prepared by providing nickel-containing fabrics with analuminum layer, the latter preferably being applied by immersing saidfabrics in aluminum melts at 600 to 700° C. The aluminum layer has athickness of at least 100 μm, preferably 150 μm. The catalysts are usedin the hydrogenation of aromatic amines.

In “Commercial Application of Cathode Coatings in Electrolytic ChlorineCells”, T. A. Liederbach et al. describe the production of nickelelectrodes in the form of wire gauzes or sheets by electroplating. Inthis process, nickel and zinc are deposited electrolytically from asolution containing ions of these metals. Electrodes of similarperformance characteristics are obtained from metal powders by theplasma spray process. Typical thicknesses of the catalytically activelayer are 250 to 300 μm. Electrodes of this type are employed inchlor-alkali electrolysis.

DE-A-37 02 138 discloses electrodes produced from Raney nickel powders.These powders are intimately mixed with another alloy, used to store H₂,and with poly-tetrafluoroethylene powder. The resulting mixture isprocessed to a coherent network by compression and rolling. Analternative possibility is to compress the mixture onto an expandedmetal to give electrodes with a layer thickness of 1 mm. Theseelectrodes are used for the storage and electrochemical scission ofhydrogen.

Finally, U.S. Pat. No. 481,440 describes a Raney nickel electrodeapplied to a graphitized paper support. This support is coated by plasmacoating with alloy powder to give layers with a thickness of 1 to 10 mm.

The Raney nickel catalysts described in the prior art generally exhibita high hydrogenating activity, but their abrasion resistance isinadequate for some uses. This is the case, for instance, whencolorless, optically clear liquids of high viscosity are subjected tohydrogenation or dehydrogenation reactions using Raney nickel catalysts.This often reveals abrasion originating from the Raney alloy catalyst.Depending on the type of this catalyst, the abraded material can becoarsely to finely particulate, as is the case for powder catalysts andcatalysts obtained by the electrochemical deposition of metals. Even inthe case of 1 mm thin layers on woven fabric, the abrasion of very fineparticles is still observed, which may not be tolerable for all productrequirements.

It is therefore an object of the present invention to provide Raneyalloy catalysts which have a high hydrogenating activity and anextremely high abrasion resistance, even on contact with viscousliquids.

We have found that this object is achieved by Raney alloy catalystsapplied to a support, wherein the Raney alloy layer has a thickness of0.2 to 100 μm.

The catalyst generally takes the form of tape, film, woven fabric orknitted fabric. These catalyst tapes are preferably coated by electronbeam vaporization under reduced pressure.

Different metals can be used according to the desired Raney alloy.Aluminum is used in every case. The other metal needed to prepare aRaney alloy is selected from the group consisting of nickel, cobalt andcopper, nickel being preferred.

If desired, the metals can additionally contain one or more promotermetals, for example iron, chromium, molybdenum or boron.

To coat the support materials, the active component, i.e. aluminum, andthe other metal used to prepare the desired Raney alloy, especiallynickel, as well as the promoter metal if desired, are vaporized underreduced pressure and condensed uniformly onto the support. Thevaporization is effected by the conventional methods known to thoseskilled in the art, for example by means of heat, by electron beamvaporization, by sputtering or by combinations of these methods. Thecoating is preferably carried out by electron beam vaporization. Thecondensation is preferably effected by the methods disclosed in U.S.Pat. No. 4,686,202 or EP564 830.

The resulting layers of vapor-deposited metal are extremely thin, beingin the range 0.1 μm to 50 μm, preferably 1 μm to 10 μm, in the case ofaluminum. The layer thicknesses of the other metals used to prepare theRaney alloy depend on the stoichiometry of the active Raney phase to beprepared. In the case of nickel, the metal layer has a thickness of 0.1μm to 10 μm, preferably 0.5 μm to 5 μm.

The support can be coated in such a way that several layers of themetals used are applied alternately. Total layer thicknesses of approx.100 μm are achieved in this way. These layer thicknesses are well belowthose achievable by the processes described in the prior art, which havevalues of about 100 to 15,000 μm. The catalysts according to theinvention therefore have metal layers with an extremely low total weightranging from approx. 1 to 20 g aluminum/m² fabric or 1 to 3 g nickel/m²fabric. These values also apply to cobalt and copper. The specific totalweight of the resulting metal layers from which the Raney alloy isformed ranges from 0.1 to 10 g/m² fabric.

The support materials used are preferably metals, one reason for thisbeing their advantageous mechanical properties. Another advantage,however, is the fact that they can be roughened prior to coating. Thisis effected by surface tempering, for which the metal supports areheated in an oxygen-containing atmosphere, for example air, over aperiod of 30 minutes to 24 hours, preferably 1 to 10 hours, thetemperatures used being from 700 to 1100° C., preferably 800 to 1000° C.It has been found that the activity of the catalyst can be controlled bythis kind of pretreatment.

Metals which are preferably used as support materials are stainlesssteels of material no. 1.4767, 1.4401, 2.4610, 1.4765, 1.4847 and 1.4301(designation according to “Stahleisenliste”, 8th edition, pages 87, 89and 101, published by Verein deutscher Eisenhüttenleute, VerlagStahleisen mbH, Düsseldorf 1990).

Other preferred metals for production of the support materials are iron,nickel or copper.

However, the list of materials suitable for the support is notrestricted to metals. Inorganic materials or dielectrics can also beused instead of metals to produce the supports, examples being ceramic,aluminum oxide, silicon dioxide, preferably woven fabric made ofasbestos substitutes, or combinations of these materials. Carbon fibersare also suitable. Organic plastics can also be used, examples of suchmaterials being polyamides, polyesters, polyvinyl compounds,polyethylene, polypropylene and polytetrafluoroethylene. All thesenon-metallic materials are used in a similar way to the metals in theform of knitted fabrics, woven fabrics or films.

The catalyst tapes obtained by the process according to the inventionhave a metal layer consisting of the appropriate Raney alloy, which iscompletely homogeneous and forms neither pores nor particles.

Said materials are used as supports in the form of films, knittedfabrics or woven fabrics. In one preferred embodiment, the supports arecorrugated or crimped, for example by gear rolling. The corrugationsobtained preferably have a pitch of 0.5 to 10 mm.

The catalyst tapes obtained after coating still have to undergo a heattreatment in order to be able to form the active Raney alloy phases. Inthe case of Raney nickel, these phases can be expressed approximately bythe formula Ni₂Al₃ or NiAl₃. The heat treatment is carried out attemperatures of 500 to 600° C. for 10 to 60 minutes under an inert gasatmosphere, examples of possible inert gases being nitrogen, argon orhydrogen.

In one variant of the invention, finished Raney alloys, preferably Raneynickel, can be vapor-deposited directly onto the support, therebydispensing with the tempering step. The Raney nickel layer is preferablyprepared by sputtering with a roll coater, the layer thicknesses of theresulting Raney alloys ranging from 1 μm to 50 μm and the preferredthickness being 1 μm.

The catalysts obtained according to the invention, applied to films orwoven or knitted tapes, can be formulated by the conventional techniquesinto packings or monoliths which can advantageously be used inhydrogenations or dehydrogenations. A large number of different packingstructures are known from distillation and mixing technologies, anexample being canal structures for gas-liquid exchange. Such structuresare described for example in EP-A-482 145 and WO 97/02890. Monolithicpackings of this type can be produced to particular advantage with thecatalyst fabrics according to the invention, whose particularlyabrasion-resistant, ultrathin layers allow them to be mechanicallytransformed into any desired shape.

The supported catalysts according to the invention can easily beactivated. At low temperatures, preferably of 20° C. to 40° C., thealuminum can be dissolved out with 1 to 20% lye, generally NaOH, toexpose the active alloy phase. The treatment with lye is only carriedout over a short period, preferably of 1 to 20 minutes.

By virtue of their abrasion resistance, the supported catalystsaccording to the invention are particularly suitable for thehydrogenation or dehydrogenation of viscous liquids on which there arehigh demands in respect of purity and optical clarity. It has been foundthat the catalysts according to the present invention are particularlysuitable for improving the color index of polyhydric alcohols byhydrogenation. It is particularly preferred to employ the catalystsaccording to the invention in the process disclosed in the German patentapplication entitled “Improving the color index of polyhydric alcoholsby hydrogenation”, reference no. 199 63 442.4 (Applicant: BASF AG).

The patent application will now be illustrated in greater detail in theExamples below:

EXAMPLE 1

A woven wire fabric made of material no. 1.4767, with a mesh size of0.18 mm and a wire diameter of 0.112 mm, was annealed in air at 900° C.for 3 hours. After cooling, the support fabric roughened in this way wasthen vapor-plated on both sides in an electron beam vaporization unit,initially at 10⁻⁶ Torr, first with a 0.2 μm thick layer of aluminum andthen, under the same conditions, with a 0.044 μm thick layer of nickel.This process was repeated continuously until the total layer thicknessreached 1.2 μm. After the tempering step for 3 hours under a nitrogenatmosphere, two monoliths with a height of 200 mm and a diameter of 21.5mm were formed from the catalyst fabric. This was done by taking onesmooth strip of fabric and one strip of fabric which had been corrugatedbeforehand by means of a gear roller, combining them, rolling them upand fixing them together by spot welding along the outside edge. Themonolithic Raney nickel film catalyst obtained was placed in a 60 cmlong reactor tube, where it was treated for 15 minutes with 10% sodiumhydroxide solution, which was then removed by washing with water.

EXAMPLE 2

A loop reactor was filled with 500 g of HDLIN(hydro-dehydrolinalool=3,7-dimethyloct-1-yn-3-ol). By the liquid phasemethod with recycling, the liquid was passed over the catalyst preparedaccording to Example 1, the cross-sectional loading being 200 m³/m²/h.Hydrogen under a pressure of 1.1 bar was circulated simultaneously withthe liquid stream. The reaction temperature was 80° C. The resultsobtained are listed in the Table below:

Overall conversion t/min % HDLIN¹ % HLIN¹ % THLIN¹ of HDLIN 0 99.70 0.000.00 0.00 30 96.33 1.57 1.81 5.18 60 92.74 3.17 3.80 10.76 90 89.72 4.525.49 15.47 120 86.44 5.99 7.30 20.56 ¹determined by gas chromatography(from the peak area) HDLIN = hydro-dehydrolinalool HLIN = hydrolinaloolTHLIN = tetrahydrolinalool

The results given in the Table show that the film catalyst according tothe invention was capable of hydrogenating a total of 50 g/h ofunsaturated alcohols to hydrolinalool and tetrahydrolinalool. Thiscorresponds to a conversion of approx. 0.33 mol/h or a space-time yieldof 0.35 kg/l_(catalyst)/h. 0.112 m² of film catalyst was used in theexperiment. From the specific weight of Raney nickel catalyst used,which was 8.6 g/m², it is seen that only 0.963 g of Raney nickel alloywas present in the reactor. The specific activity was thus 2.9 mol/m²/h.No abrasion whatsoever could be established, either on the product or inthe reactor.

EXAMPLE 3

A Raney nickel film catalyst obtained according to Example 1 was used inthe hydrogenation of 1 kg of trimethylolpropane which had been obtainedaccording to WO 98/28253 and had an APHA color index of 26 afterdistillation. The hydrogenation was carried out at a hydrogen pressureof 1.1 bar and a temperature of 140° C. After a reaction time of 15minutes, it was possible to observe an improvement in the APHA colorindex to ≦6.

1. A Raney alloy catalyst, comprising a dielectric as support and aRaney alloy layer containing aluminum and an additional metal, whereinthe Raney alloy is applied to the support as a layer having a thicknessof 0.01 to 100 μm and a total weight of from 0.1 to 20 g Al/m² support,and which catalyst is prepared by a process comprising providing thesupport, the aluminum, and the additional metal, vaporizing the aluminumand the additional metal under reduced pressure, and coating the supportwith the aluminum and the additional metal by depositing the vaporizedaluminum and the vaporized additional metal uniformly onto the support.2. A catalyst as claimed in claim 1 which, in addition to aluminum,contains at least one metal selected from the group comprising ofnickel, cobalt and copper as other components, optionally together witha promoter metal selected from the group consisting of iron, chromium,molybdenum and boron.
 3. A catalyst as claimed in claim 2, wherein theadditional metal is nickel.
 4. A catalyst as claimed in claim 3, whereinthe Raney alloy layer has a total weight from about 1 to 20 g Al/m²support in form of a knitted or woven fabric and from 1 to 3 g Ni/m²support in form of a knitted or woven fabric.
 5. A catalyst as claimedin claim 3, wherein the layer thickness of the vapor-deposited aluminumranges from 0.1 to 50 μm and of the vapor-deposited nickel from 0.1 to10 μm.
 6. A catalyst as claimed in claim 5, wherein the thickness of thealuminum layer ranges from 1 μm to 10 μm and for the nickel layer from0.5 μm to 5 μm.
 7. A catalyst as claimed in claim 1, wherein the Raneyalloy layer has a total weight of 0.1 to 10 g/m² support in form of aknitted or woven fabric.
 8. A catalyst as claimed in claim 1, whereinthe coating is carried out by means of heat, by electron beamvaporization, by sputtering or by combinations of these methods.
 9. Acatalyst as claimed in claim 8, wherein the coating is carried out byelectron beam vaporization.
 10. A catalyst as claimed in claim 1,wherein the support is selected from the group consisting of pretreatedmetals, ceramic, aluminum oxide, silicon dioxide, fabrics made ofasbestos substitutes, carbon fibers, organic plastics and combinationsof said materials, wherein said metals are selected from the groupconsisting of iron, nickel, copper and steel having material Nos.1.4767, 1.4401, 2.4601, 1.4765, 1.4847 and 1.4301, and said metals arepretreated by heating in an oxygen containing atmosphere.
 11. A catalystas claimed in claim 10, wherein the metal used as a support material istempered in an oxygen-containing atmosphere at temperatures of 700 to1100° C. over a period of 30 minutes to 24 hours before coating thesupport with the vaporized aluminum and the vaporized additional metal.12. A catalyst as claimed in claim 11, wherein the metal is tempered attemperatures of 800 to 1000° C. and over 1 hour to 10 hours.
 13. Acatalyst as claimed in claim 10, wherein the organic plastics areselected from a group consisting of polyamides, polyesters, polyvinylcompounds, polyethylene, polypropylene and polytetrafluoroethylene. 14.A catalyst as claimed in claim 1 in the form of a catalyst strip or amonolithic catalyst packing produced from this catalyst strip.
 15. Aprocess for the activation of a catalyst as claimed in claim 1, whereinthe catalyst is extracted with a base at low temperatures over a shortperiod.
 16. A process as claimed in claim 15, wherein the catalyst isextracted at 20 to 400° C. over 1 to 20 minutes.
 17. A process for thepreparation of a catalyst as claimed in claim 1, wherein the aluminumand the additional metal are applied alternately to the support byvaporization and the catalyst obtained is optionally transformed to thedesired shape.
 18. A process as claimed in claim 17, wherein thevaporization is effected by means of heat, by electron beamvaporization, by sputtering or by a combination of these methods.
 19. Aprocess as claimed in claim 18, wherein the vaporization is effected byelectron beam vaporization.
 20. A process for the preparation of acatalyst as claimed in claim 1, wherein a Raney alloy containing thealuminum and the additional metal is applied to the support byvaporizing the Raney alloy and subsequently condensing the vaporizedRaney alloy onto the support.
 21. A process as claimed in claim 20,wherein the vaporization is effected by means of heat, by electron beamvaporization, by sputtering or by a combination of these methods.
 22. Aprocess as claimed in claim 21, wherein the vaporization is effected byelectron beam vaporization.